Bud Rot vs. Mold: How To Identify & Treat

It doesn’t matter which stage you’re at in the growth process. Finding mold growth on cannabis flower can be devastating. And the same goes for bud rot down beneath.

Both signs are indicators that your plant is literally screaming for help. So what happens when marijuana plants experience these issues, and how can you help? Hopefully, you can catch mold and bud rot early, as the best way to avoid infected plants is prevention. If you’re not careful, they can ruin your entire crop.

Let’s take a closer look at the difference between cannabis bud rot vs mold, and how to save those precious plants once infected.

Bud rot has a scientific name: Botrytis cinerea, aka gray mold. This is a specific type of fungal infection that attacks cannabis flowers.

While all bud rot is mold, not all mold on cannabis is bud rot. Why should you know the difference? Because each has a unique treatment approach to ensure you nip the infection in the bud (pun intended).

Botrytis bud rot usually starts forming inside the densest parts of cannabis buds where air circulation is worst. It spreads out and eventually turns your once-vibrant cannabis buds into a gray, mushy mess that produces spores. Those spores can travel like wildfire and contaminate your entire grow space.

There are a few environmental factors that affect what causes bud rot in weed. Even just a few of them can do damage. But all of them together? Disastrous:

1. Excess moisture: High humidity (above 60% during flowering) creates ideal conditions for fungus spores to germinate
2. Poor air circulation: Dense, leafy plants without good airflow trap humid air around buds, which encourages mold growth
3. Warm temperatures: The 60–80°F (15–27°C) range, when paired with humidity, creates ideal conditions for mold to spread
4. Dense bud structure: Thicker buds trap moisture inside, creating microclimates that mold loves
5. Plant damage: Broken branches, insect damage, or other injuries provide entry points for spores

Outdoor growers have to pay even closer attention to challenges from rain, morning dew, and fluctuating temperatures. On the other hand, indoor growers have to monitor humidity levels and air movement in their grow room.

Catching bud rot early is crucial for saving your harvest. Look for these telltale signs:

• Early stages: Leaves on buds turning yellow or brown while the surrounding foliage is green
• Middle stages: Dark purple or brown discoloration within the buds
• Advanced stages: Gray fuzzy mold visible on the outside of buds, often with white, powdery mildew

What does bud rot look like? Take a test bud and gently pull apart your flower. Bud rot starts from the inside, with the stem becoming brown and soft. Healthy bud stems should be green and firm.

What does bud rot smell like? Infected buds stink, and not in a good way. They have a musty, sweet odor. Some describe it as smelling like wet hay or a damp basement. In most cases, you’ll notice this off-putting smell before any visuals appear. It’s a very important warning sign.

Bud rot attacks the flowers and starts inside the cannabis bud. That said, mold can affect many different parts of cannabis plants and wreak havoc if left unchecked. Here’s how to tell the difference:

Powdery Mildew:

• Looks like white powder on fan leaves and bud leaves
• Develops on the surface rather than inside the plant material
• Spreads quickly across foliage but doesn’t immediately destroy buds
• More common during the vegetative stage, but it can continue into the flowering stage

Root Rot:

• Arguably smells the worst, like decay
• Often caused by overwatering and poor drainage
• Plants show stunted growth and yellowing leaves
• No visible mold on the upper portions of plants at first
• Affects the root system and causes wilting/nutrient deficiencies

White Mold (Sclerotinia):

• Creates cottony white mold on stems and branches
• More common in outdoor grows, especially in humid climates
• Causes hanging branches to wilt, and eventually the whole plant to collapse

Aspergillus:

• Very dangerous mold
• Found on dried cannabis
• Often appears greenish or black
• Usually only visible under magnification
• Can cause serious respiratory issues if smoked

There’s likely still time to save your precious cannabis plants from more dangerous mold spores and marijuana bud rot. The key? Immediate action. Here’s what to do with bud rot:

1. Remove Infected Parts

• Find and remove all infected buds completely
• Cut at least 1 inch below any visible infection
• Dispose of moldy buds and infected material away from your grow area
• Disinfect tools after each cut to prevent spreading spores

2. Improve Growing Conditions

• Lower humidity to below 50% in your grow space
• Increase air circulation with fans
• Make sure there’s proper spacing between plants
• Remove excess fan leaves to improve airflow
• Adjust watering to avoid wet buds and extra moisture

3. Try Organic Treatments

• Neem oil on unaffected plants (not recommended for late flowering)
• Hydrogen peroxide solutions (diluted to 3%) as a preventative spray
• Potassium bicarbonate-based organic fungicides for early-stage prevention
• Compost teas with beneficial microbes to compete with harmful fungi

4. Harvest Plants Early If Necessary 

If you come across bud rot during the late flowering stage:

• Try harvesting early if necessary
• Scan the entire plant and focus on saving healthy buds
• Carefully inspect all harvested material during the drying process
• Dispose of any suspicious buds to avoid contaminating your entire harvest

Reminder: Once a bud shows signs of rot, there’s no going back. She sadly can’t be saved, and smoking bud rot flower poses serious health risks. The key? Prevention.

Preventative measures are your best bet. Since mold spores spread quickly, it’s much easier to spend effort avoiding them beforehand rather than fighting them off later. Here are the best ways to prevent bud rot and mold:

Control Humidity:

• Aim for 40-50% humid conditions during flowering
• Use dehumidifiers in your grow room if needed
• Keep proper ventilation with intake and exhaust fans
• Consider automating humidity control with technology

Improve Air Circulation:

• Install oscillating fans to keep air moving around all plants
• Prune lower branches and excess foliage to increase airflow
• Have proper spacing between plants
• Support heavy branches to prevent them from touching soil or other plants

Careful Watering Practices:

• Water at the base of plants instead of over foliage
• Water early in the day so plants can dry before night
• Don’t overwater the plant and ensure proper drainage
• Try drip irrigation systems to reduce as much moisture as possible on foliage

Basic Prevention:

• Regularly inspect flower, especially inside the thickest buds
• Use protective sprays during the vegetative stage (before flowers develop)
• Silica supplements can strengthen plant cell walls
• Beneficial bacteria and fungi help create a protective microbiome

Environmental Controls:

• Protection from rain for outdoor plants (covers and tarps)
• Choose growing spots with natural air movement
• Ensure proper drainage

Some cannabis strains naturally resist mold and bud rot better than others. Try these mold-resistant cannabis strains if you grow in humid conditions:

• Durban Poison
• Northern Lights
• Dutch Treat
• Super Silver Haze
• Blue Dream

What happens if you smoke bud rot?

Serious health issues can occur if you smoke moldy weed, including buds with bud rot. Those issues include respiratory infections, lung inflammation, allergic reactions, and more. Never smoke marijuana bud rot. The mold spores can do incredible damage when inhaled.

When does bud rot occur?

Bud rot usually starts during the flowering stage when buds are dense enough to trap moisture. The risk basically doubles during the last 2-3 weeks before harvest when buds are at their densest.

How fast does bud rot spread?

Too fast for comfort. Once bud rot starts, it can infect an entire bud within 2-3 days and spread through a plant within a week. Head out for vacation at the wrong time, and you can kiss your harvest goodbye.

How often should I inspect my plants for mold?

Check cannabis plants for mold weekly during the vegetative stage. Once flowering kicks in, up it to every 2-3 days. In the last few weeks before harvest, we suggest taking daily inspections. This is especially important if you’re dealing with denser buds and periods of high humidity.

Does freezing weed kill mold?

Sadly, no. The freezer is no help once your plants have reached the point of no return. Freezing doesn’t kill mold or fungus spores. It makes them dormant, but the mold usually continues growing once it’s back at room temperature.

Can you save a plant with bud rot?

It really depends on how bad the situation is. You definitely can’t save buds already infected with bud rot, but you can potentially save the rest of the plant by acting fast and removing all infected parts. Be sure to cut well below the visible infection and dispose of infected material away from your grow area to prevent spreading spores.

How can I tell the difference between trichomes and mold?

Good question. They can both look white, so here’s how to tell the difference. Trichomes will be clear, cloudy, or amber crystal-like structures (you can see their shapes better with magnification). They look like tiny mushrooms with stems and caps. Mold will look fuzzy, web-like, or powdery without a neat structure. Trichomes cover the surface evenly, while mold grows in irregular patches.

Can mold grow on dried and cured weed?

It absolutely can, if it’s not stored properly. To prevent mold when storing weed, ensure you have the following: humidity between 58-62% with humidity packs, airtight containers, and access to a cool, dark place.

Can mold grow inside sealed jars or containers?

Definitely. The key to avoiding this? Drying cannabis properly. If it isn’t, mold can develop fast. It’s likely developing because the flower is above 12% moisture content, or the containers are being stored in warm places. This is also why curing with regular burping is a must.

What’s the ideal humidity to prevent mold in a grow room?

Here’s a quick visual to better understand the ideal humidity level to prevent mold:

• Vegetative growth: 40-60%
• Early flowering: 40-50%
• Late flowering: 30-40%
• Drying room: Start at 60% and gradually reduce to 50%

Now that you’ve got the rundown on the causes of bud rot vs. other types of mold, we wish you the absolute best in your harvest. Start with prevention, and do yourself (and your plants) a favor in the long run.